Frequency deviation detecting circuit and measuring apparatus using the frequency deviation detecting circuit

Abstract

A hardness measuring apparatus in which a frequency deviation detecting circuit is used has a contact element, an oscillator, a self-oscillating circuit and a gain variation compensating circuit. The self-oscillating circuit feeds back oscillation information of the oscillator to generate a resonant state. The gain variation compensating circuit is disposed in the self-oscillating circuit. The gain variation compensating circuit has a central frequency different from that of the self-oscillating circuit, and increases gain in response to a change in frequency.

I claim: 
     
       1. A frequency deviation detecting circuit comprising: an oscillator for generating a mechanical oscillation;   a self-oscillating circuit for feeding back oscillation information of the oscillator, and for generating a resonant state in the oscillator, wherein the oscillator and the self-oscillating circuit form an electromechanical oscillation system; and   a gain variation compensating circuit which is disposed in the self-oscillating circuit, has a central frequency different from that of the self-oscillating circuit, and increases gain of the self-oscillating circuit in response to a change in frequency of the electromechanical oscillation system; wherein the effective resonance frequency band of the electromechanical oscillation system is expanded.     
     
     
       2. A frequency deviation detecting circuit according to claim 1, wherein the gain variation compensating circuit comprises means, including a phase transfer function, for adjusting the difference between the input and output phases, called phase difference, of the self-oscillating circuit to zero, and for promoting feedback oscillation, shifting the frequency so that the phase difference becomes zero, and increasing the gain. 
     
     
       3. A hardness measuring apparatus for obtaining hardness information of a subject comprising: a contact element adapted to contact a subject;   an oscillator for oscillating the contact element;   a self-oscillating circuit which feeds back oscillation information of the oscillator oscillating the contact element in contact with the subject to generate a resonant state in the oscillator, wherein the oscillator and the self-oscillating circuit form an electromechanical oscillation system; and   a gain variation compensating circuit which is disposed in the self-oscillating circuit, has a central frequency different from that of the self-oscillating circuit, and increases gain of the self-oscillating circuit in response to a change in frequency of the electromechanical oscillation system; wherein the effective resonance frequency band of the electromechanical oscillation system is expanded.     
     
     
       4. A hardness measuring apparatus according to claim 3, wherein the hardness of the subject is measured using a change in the frequency of the electromechanical oscillation system. 
     
     
       5. A hardness measuring apparatus according to claim 3, wherein the hardness of the subject is measured using a change in the phase of the electromechanical oscillation system. 
     
     
       6. A hardness measuring apparatus according to claim 3, wherein the gain compensating circuit increases the gain with a decrease in frequency, and the effective resonance frequency band of the electromechanical oscillation system is expanded in a frequency range used for measuring the hardnesses of soft subjects. 
     
     
       7. A hardness measuring apparatus according to claim 3, wherein the oscillator is any one of a piezoelectric ceramic oscillator, layered ceramic oscillator, PVDF-based oscillator, magnetostrictive element, bimorph oscillator, quartz oscillator or surface acoustic wave (SAW) element. 
     
     
       8. A hardness measuring apparatus according to claim 3, wherein the self-oscillating circuit has an amplifying circuit for amplifying the oscillation information of the oscillator. 
     
     
       9. A hardness measuring apparatus according to claim 8, wherein the gain variation compensating circuit is disposed between an output terminal of the oscillator and an input terminal of the amplifying circuit of the self-oscillating circuit, or between an output terminal of the amplifying circuit of the self-oscillating circuit and an input terminal of the oscillator. 
     
     
       10. A hardness measuring apparatus according to claim 3, wherein the gain variation compensating circuit comprises any of a band-pass filter circuit, a low-pass filter circuit, a high-pass filter circuit, a notch filter circuit, an integrating circuit, a differentiating circuit, a peaking amplifying circuit, an active filter circuit or a passive filter circuit. 
     
     
       11. A hardness measuring apparatus according to claim 3, wherein the gain variation compensating circuit comprises means, including a phase transfer function, for adjusting the difference between the input and output phases, called phase difference, of the self-oscillating circuit to zero, and for promoting feedback oscillation, shifting the frequency so that the phase difference becomes zero, and increasing the gain. 
     
     
       12. A hardness measuring apparatus according to claim 3, wherein hardness information of the subject is obtained by using one of a change in the frequency of the electromechanical oscillation system and a change in a phase of the electromechanical oscillation system, and the subject is a biological tissue, and the contact element is adapted to come into contact with the biological tissue when the hardness of the biological tissue is measured. 
     
     
       13. A hardness measuring apparatus according to claim 12, wherein the biological tissue is any of skin, internal organs, body cavities, bones, teeth or nails, and its hardness is measured. 
     
     
       14. A hardness measuring apparatus according to claim 12, further comprising: a main probe in which the oscillator is contained, and the contact element is fixed; and   a monitor for displaying hardness information based on the oscillation information.   
     
     
       15. A hardness measuring apparatus according to claim 14, further comprising: a fiberscope unit, wherein an observation image obtained by the fiberscope unit is displayed on the monitor.   
     
     
       16. A hardness measuring apparatus according to claim 14, wherein the contact element comprises a contact needle, and an outer needle disposed around the contact needle is placed at the tip portion of the main probe for puncturing a biological tissue. 
     
     
       17. A hardness measuring apparatus according to claim 14, wherein the tip portion of the main probe is formed by a soft tube. 
     
     
       18. A hardness measuring apparatus for obtaining hardness information of a subject comprising: a contact element in contact with a subject;   an oscillator for oscillating the contact element;   a self-oscillating circuit which feeds back oscillation information of the oscillator oscillating the contact element in contact with the subject to generate a resonant state in the oscillator, wherein the oscillator and the self-oscillating circuit form an electromechanical oscillation system;   a gain variation compensating circuit which is disposed in the self-oscillating circuit, has a central frequency different from that of the self-oscillating circuit, and increases gain in response to a change in frequency of the electromechanical oscillation system; and   a frequency measuring circuit for detecting a change in the frequency of the electromechanical oscillation system.   
     
     
       19. A hardness measuring apparatus according to claim 18, further comprising: a detecting element for detecting the oscillation information of the oscillator, wherein the oscillator comprises a layered piezoelectric ceramic oscillator formed by stacking a plurality of piezoelectric ceramic layers, and the detecting element comprises a film-shaped bimorph oscillator.   
     
     
       20. A hardness measuring apparatus according to claim 18, further comprising: a detecting element for detecting the oscillation information of the oscillator, wherein both the oscillator and detecting element comprise a layered piezoelectric ceramic oscillator formed by stacking a plurality of piezoelectric ceramic layers.   
     
     
       21. A hardness measuring apparatus according to claim 18, further comprising a detecting element for detecting the oscillation information of the oscillator, wherein both the oscillator and detecting element comprise a film-shaped piezoelectric material. 
     
     
       22. A hardness measuring apparatus for obtaining hardness information of a subject comprising: a contact element adapted to contact a subject;   an oscillator for oscillating the contact element;   a phase lock loop circuit which feeds back oscillation information of the oscillator oscillating the contact element in contact with the subject to generate a resonant state in the oscillator, wherein the contact element, the oscillator and the phase lock loop circuit form an electromechanical oscillation system; and   a gain variation compensating circuit which is disposed in the phase lock loop circuit, has a central frequency different from that of the phase lock loop circuit, and increases gain of the phase lock loop circuit in response to a change in frequency of the electromechanical oscillation system; wherein the effective resonance frequency band of the electromechanical oscillation system is expanded.     
     
     
       23. An acceleration measuring apparatus for measuring a change in the acceleration of a moving substance comprising: an oscillator which is placed on the moving substance, and generates a mechanical oscillation;   a self-oscillating circuit which feeds back oscillation information of the oscillator to generate a resonant state in the oscillator, wherein the oscillator and the self-oscillating circuit form an electromechanical oscillation system; and   a gain variation compensating circuit which is disposed in the self-oscillating circuit, has a central frequency different from that of the self-oscillating circuit, and increases gain of the self-oscillating circuit in response to a change in frequency of the electromechanical oscillation system; wherein the effective resonance frequency band of the electromechanical oscillation system is expanded.     
     
     
       24. A fluid viscosity measuring apparatus for measuring a change in the viscosity of a fluid comprising: any of an oscillator for generating oscillation in a fluid and an oscillator for oscillating a fluid contacting element put in the fluid;   a self-oscillating circuit which feeds back oscillation information of the oscillator to generate a resonant state in the oscillator, wherein the oscillator and the self-oscillating circuit form an electromechanical oscillation system; and   a gain variation compensating circuit which is disposed in the self-oscillating circuit, has a central frequency different from that of the self-oscillating circuit, and increases gain of the self-oscillating circuit in response to a change in frequency of the electromechanical oscillation system; wherein the effective resonance frequency band of the electromechanical oscillation system is expanded.     
     
     
       25. A fluid pressure measuring apparatus for measuring a change in the pressure of a fluid comprising: a fluid contacting element whose shape is changed in response to the pressure of a fluid;   an oscillator which generates oscillation, and the position of which is moved in response to the change in the pressure of the fluid;   a self-oscillating circuit which feeds back oscillation information of the oscillator to generate a resonant state in the oscillator, wherein the oscillator and the self-oscillating circuit form an electromechanical oscillation system; and   a gain variation compensating circuit which is disposed in the self-oscillating circuit, has a central frequency different from that of the self-oscillating circuit, and increases gain of the self-oscillating circuit in response to a change in frequency of the electromechanical oscillation system, wherein the effective resonance frequency band of the electromechanical oscillation system is expanded.     
     
     
       26. A measuring apparatus according to claim 22, wherein the gain variation compensating circuit has a phase transfer function of adjusting the difference between the input and output phases, called phase difference, of the self-oscillating circuit to zero, and of promoting feedback oscillation, shifts the central frequency so that the phase difference becomes zero, and increases the gain.